High-efficiency solar cells on phosphorus gettered multicrystalline silicon substrates

Abstract

Measurements of the dislocation density are compared with locally resolved measurements of carrier lifetime for p-type multicrystalline silicon. A correlation between dislocation density and carrier recombination was found: high carrier lifetimes (>100 μs) were only measured in areas with low dislocation density (<105cm 2), in areas of high dislocation density (>106 cm-2) relatively low lifetimes (<20 μs) were observed. In order to remove mobile impurities from the silicon, a phosphorus diffusion gettering process was applied. An increase of the carrier lifetime by about a factor of three was observed in lowly dislocated regions whereas in highly dislocated areas no gettering efficiency was observed. To test the effectiveness of the gettering in a solar cell manufacturing process, five different multicrystalline silicon materials from four manufacturers were phosphorus gettered. Base resistivity varied between 0.5 and 5 Ω cm for the boron- and gallium-doped p-type wafers which were used in this study. The high-efficiency solar cell structure, which has led to the highest conversion efficiencies of multicrystalline silicon solar cells to date, was used to fabricate numerous solar cells with aperture areas of 1 and 4 cm2. Efficiencies in the 20% range were achieved for all materials with an average value of 18%. Best efficiencies for 1cm2 (20.3%) and 4 cm2 (19.8%) cells were achieved on 0.6 and 1.5 Ω cm, respectively. This proves that multicrystalline silicon of very different material specification can yield very high efficiencies if an appropriate cell process is applied. Copyright © 2006 John Wiley & Sons, Ltd.